What did charles darwin hypothesize about the origin of bipedalism?

Charles Darwin has the first or the origin of the bipedalism hypothesis. Human beings are compared to apes and he also suggested enormous brain and upright locomotion were link. He also suggested human evolved into larger brains when still ape-like-tree-dwellers. Humans are bipedal because they have free hands to carry and manipulate tools and having tool-use, lost their project canning.